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  • Erick A. Mosteller

Unraveling the Universe: Comparing the Causal Set Theory, Big Bang, and String Theory

Causal set theory, big bang theory, and string theory are all significant concepts in theoretical physics, each with its own unique approach to understanding the universe. Comparing their mathematical correctness requires exploring the core principles of each theory, their mathematical foundations, and how they address key questions in physics.

Causal Set Theory

Core Principles: Causal Set Theory (CST) is an approach to quantum gravity, an area of theoretical physics aiming to unify the theories of general relativity and quantum mechanics. This theory stands as one of several competing models in the ongoing quest to describe the fundamental structure of space-time at the Planck scale, where the effects of both quantum mechanics and gravity are significant. Causal Set Theory was proposed in the late 20th century, drawing inspiration from the discrete nature of quantum mechanics and the causal structure inherent in general relativity. The central idea of CST is that space-time is not a smooth continuum, as suggested by general relativity, but is instead composed of discrete, indivisible elements.

CST posits that space-time is made up of a countable set of fundamental elements. This discretization is thought to naturally incorporate a scale (the Planck scale), below which the concept of space-time ceases to be meaningful. Each element in this set is causally related to others, forming a structure akin to a partially ordered set. This causal order replaces the concept of a smooth metric, which is used in general relativity to describe the geometry of space-time. Despite its discrete nature, CST aims to maintain Lorentz invariance, a foundational principle of relativity stating that the laws of physics are the same for all observers, regardless of their relative motion.

One of the key predictions of CST is the emergence of space-time geometry at large scales from the underlying discrete structure. This emergence is akin to how thermodynamic properties arise from atomic or molecular structures in statistical mechanics. Additionally, CST might provide insights into the resolution of singularities, such as those found in black holes or the Big Bang, where classical theories of gravity break down.

Mathematical Foundation: The theory is based on the principles of causality and Lorentz invariance, and it uses tools from order theory and topology. The mathematics of causal sets is discrete, which contrasts with the continuous mathematics of traditional spacetime theories. This discreteness helps to avoid some of the infinities that arise in quantum field theory and general relativity. Developing a coherent mathematical framework that encompasses both the discrete structure of causal sets and the emergence of continuum properties is a significant challenge. As with many theories of quantum gravity, testing the predictions of CST is difficult with current experimental technology. The effects it describes occur at scales and energies far beyond what can currently be observed or measured. CST competes with other theories of quantum gravity like Loop Quantum Gravity, String Theory, and others. Each of these theories has its own strengths and weaknesses, and there is no consensus yet on which, if any, provides the correct description of quantum gravity.

Advantages: The primary advantage of causal set theory is its potential to unify general relativity and quantum mechanics. By treating spacetime as discrete, it naturally incorporates a quantum theory of gravity. The theory is also relatively minimalistic, not requiring extra dimensions or entities beyond the causal sets themselves.

Big Bang Theory

Core Principles: The Big Bang Theory posits that the universe began as an extremely hot and dense point, roughly 13.8 billion years ago. This initial state, often referred to as a singularity, then rapidly expanded and cooled. This expansion is not like an explosion of a bomb in space; rather, it's the expansion of space itself. The tenets of the Big Bang hang their theories on the following observations. First is Cosmic Microwave Background Radiation (CMBR), discovered by Arno Penzias and Robert Wilson in 1965, CMBR is a faint glow left over from the early universe. It's considered a relic of the Big Bang, providing a snapshot of the universe when it was just 380,000 years old. Second is Hubble's Law and Redshift. In the 1920s, Edwin Hubble observed that galaxies are moving away from each other, implying the universe is expanding. This expansion is evidenced by the redshift of light from distant galaxies, fitting the prediction of the Big Bang Theory. And lastly is the Abundance of Light Elements. The Big Bang Theory explains the relative proportions of light elements (hydrogen, helium, lithium) in the universe. Nuclear reactions in the first few minutes of the universe's existence led to the formation of these elements in the predicted ratios.

Mathematical Foundation: It relies heavily on the equations of general relativity and models such as the Friedmann-Lemaître-Robertson-Walker metric. The mathematics involved are primarily differential equations dealing with a continuous spacetime manifold. Einstein's theory of general relativity is fundamental to the Big Bang model. It provides the mathematical description of how gravity operates in the universe. Quantum Fluctuations in the very early universe may have led to the creation of galaxies, stars, and other structures but such fluctuations cannot be measured and therefore, are simply postulated as a possibility of how the universe formed the way did. Lastly, the Inflation Theory Proposed by Alan Guth in 1980 suggests a period of rapid expansion immediately after the Big Bang. This theory helps to explain the uniformity of the CMBR and the large-scale structure of the universe.

Advantages: The big bang theory is supported by a wide range of empirical evidence, including the cosmic microwave background, Hubble's law of cosmic expansion, and the abundance of light elements. It provides a comprehensive explanation for the observable universe. However, Dark Matter and Dark Energy constitute most of the universe's mass-energy content but remain poorly understood if understood at all, however, understanding their nature is crucial for a comprehensive picture of the Big Bang. Additionally, The Singularity and Planck Era are problematic as the laws of physics as currently understood as they break down at the singularity. The Planck Era, a fraction of a second after the Big Bang, is still shrouded in mystery. Merging our current understanding of Quantum Mechanics requires ongoing research to reconcile the Big Bang Theory with quantum mechanics, aiming for a unified theory of quantum gravity.

String Theory

Core Principles: String theory suggests that the fundamental constituents of the universe are one-dimensional "strings" rather than point particles. It includes the concept of additional spatial dimensions beyond the familiar three.

Mathematical Foundation: String theory is mathematically complex, involving advanced concepts from quantum mechanics, general relativity, and supersymmetry. It uses a variety of mathematical tools, including conformal field theory, topology, and algebraic geometry.

Advantages: String theory's main appeal is its ability to provide a framework for unifying all fundamental forces and particles. It offers potential explanations for gravity and other forces at the quantum level, something that conventional quantum field theory struggles with.

Comparing the Theories

  1. Mathematical Rigor: Causal set theory's discrete mathematics is considered more rigorous in avoiding certain paradoxes and infinities that arise in theories based on continuous spacetime. However, this comes at the cost of being less developed in terms of empirical predictions.

  2. Empirical Evidence: The big bang theory stands out for its strong empirical backing. In contrast, both causal set theory and string theory lack direct empirical evidence, making their correctness harder to evaluate solely on a mathematical basis.

  3. Unification of Physics: String theory and causal set theory both aim to unify quantum mechanics and general relativity, but they do so in radically different ways. String theory's higher-dimensional approach and causal set theory's discrete spacetime offer contrasting solutions to the problem of quantum gravity.

  4. Mathematical Complexity: String theory is often criticized for its extreme mathematical complexity and lack of predictive power, whereas causal set theory offers a simpler, more elegant framework. However, simplicity does not necessarily imply correctness.

  5. Compatibility with General Relativity: While string theory modifies general relativity by introducing additional dimensions, causal set theory remains more closely aligned with it by respecting the principles of causality and Lorentz invariance.


In determining which theory is more "mathematically correct," it is essential to consider the goals and approaches of each. Causal set theory offers a mathematically elegant and minimalistic approach but lacks empirical support. The big bang theory is empirically robust but does not address the unification of gravity with quantum mechanics. String theory attempts this unification but at the cost of significant mathematical complexity and lack of empirical predictions. Ultimately, the "correctness" of these theories may depend more on their ability to generate testable predictions and their alignment with observed phenomena, rather than purely on mathematical elegance or simplicity. As theoretical physics progresses, the insights from these theories may converge, leading to a more comprehensive understanding of the universe. As it stands right now all we have is a rough idea of what might have happened, but as more and more information is provided from the James Webb Telescope certain theories once thought solid are being destroyed and new theories need to be created to make sense of the new information. The future should bring exciting new understanding of how the universe exists and how we can better understand our unique place in this amazing vacuum structure.

Erick Mosteller is a 35-year entrepreneur and business development consultant who is passionate about elevating critical understanding through effective information. Mr. Mosteller has degrees in ethnography, business administration, and International Marketing. Mosteller believes development of the rational mind and thoughtful training of the reactive mind is the key to long lasting happiness and understanding. Stay tuned for greater insights.

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